A switch of this type is known, for example, from European patent applications EP 0696040 A1 and EP 0951039 A1, the contents and disclosure of which are fully incorporated in the scope of the present patent application, by way of reference thereto.
During the switching of high currents by switches of this type, specifically in the event of a short-circuit, high pressures in the range of 10 to 100 bar and temperatures in excess of 2300° K. typically occur in the insulating gas contained in a pressure chamber and in a return duct. In the case of very high currents, specifically in a range in excess of 250 kA and/or in switches of compact construction, temperatures of up to 3000° K. or higher may occur. As a result, the obturator of a non-return valve, configured as a metal ring, which is fitted to the outlet of the return duct to the heating chamber for the insulating gas may undergo plastic strain, such that the non-return valve is no longer capable of satisfactorily fulfilling its function.
Tests have demonstrated that plastic strain of this type can be prevented, or at least substantially reduced, by the use of an obturator of more solid construction; however, this is associated with a simultaneous increase in the inertia of the non-return valve such that, upon actuation, the closure of the return duct by raid valve is insufficiently rapid, thereby permitting the unwanted escape of insulating gas from the heating chamber.
A puffer-type circuit breaker is known from DE 29604500 U1, in which the puffer piston is coated with a layer of heat-resistant plastic, such as PTFE or polyamide, in order to provide electrical shielding in relation to the contact piece or to prevent the formation of root points for the switching arc on the puffer piston.
Accordingly, the object of the invention, is the proposal of a circuit breaker which eliminates the disadvantages described above.